The invention relates to a circuit-breaker including two contacts which are disposed in an interrupting space filled with a dielectric gas under pressure and between which an electric arc strikes during circuit-breaker opening, the circuit-breaker further including a thermal blast chamber that communicates directly with the interrupting space, and a piston-driven compression chamber that communicates with the thermal blast chamber, in which circuit-breaker the piston-driven compression chamber communicates with the interrupting space via a discharge channel that is separate from the thermal blast chamber and that is closed by a discharge valve.
Such a high-voltage circuit-breaker is known from German Patent DE-19613030. In that known circuit-breaker, the interrupting space is defined by the neck and the diverging portion of a nozzle secured to the moving contact of the circuit-breaker. When the circuit-breaker is in the closed position, the fixed contact of the circuit-breaker passes through the neck of the nozzle. The thermal blast chamber and the discharge channel open out directly in the neck of the nozzle, and the discharge valve is mounted between the piston-driven compression chamber and the discharge channel in a manner such as to prevent any gas from returning from the interrupting space to the piston-driven compression chamber. The discharge channel is connected to the neck of the nozzle in a manner such that, during circuit-breaker opening, the thermal blast chamber is put in communication with the interrupting space before the piston-driven compression chamber is put in communication with the interrupting space via the discharge channel.
When interrupting low current, the pressure of the dielectric gas increases more quickly in the piston-driven compression chamber than in the thermal blast chamber. Because of the difference between the increases in the pressures of the gas in the two chambers, the check valve that is placed in the communication channel via which the two chambers can communicate opens and the gas under increased pressure in the piston-driven compression chamber is blasted into the interrupting space through the thermal blast chamber. Unfortunately, a portion of the gas under increased pressure in the piston-driven compression chamber is also discharged into the interrupting space through the discharge channel. The effect of the gas being discharged through the discharge channel is to reduce the intrinsic capacity of the piston-driven compression chamber to extinguish an arc by blasting it.
When interrupting high current, the pressure of the gas in the thermal blast chamber increases more quickly than the pressure of the gas in the piston-driven compression chamber. Because of the difference between the increases in the pressures of the gas in the two chambers, the communication channel via which the two chambers can communicate is closed by the check valve so that it is the gas under increased pressure in the thermal blast chamber that is blasted into the interrupting space between the two contacts. When the fixed contact uncovers the mouth of the discharge channel in the neck in the nozzle, there is a risk that the electric arc might develop at the mouth of the discharge channel because of the small diameter of the neck of the nozzle, and, by heating the gases, might cause them to return from the interrupting space towards the piston-driven compression chamber. Although such return is stopped by the check valve of the discharge channel, the piston-driven compression chamber can then no longer be emptied, and the increase in the pressure of the gas in said chamber causes an opposing force that opposes the movement of the moving contact of the circuit-breaker, and can cause the circuit-breaker opening operation to be stopped undesirably.
European Patent Application EP-806049 also discloses a circuit-breaker, in which the compression piston in the piston-driven compression chamber is provided with calibrated valves which open when the increase in the pressure of the gas in the piston-driven compression chamber crosses a critical threshold. In that way, when interrupting high current, the piston-driven compression chamber is emptied via the rear of the piston, but the gas under increased pressure in said chamber is then not used for interrupting the arc, and it is therefore lost.
An object of the invention, is to provide a circuit-breaker that does not suffer from the above-mentioned drawbacks. In particular, an object of the invention is to provide a circuit-breaker in which, when interrupting low current, all of the gas under increased pressure in the piston-driven compression chamber goes through the thermal blast chamber to blast the electric arc that strikes between the two contacts of the circuit-breaker, and in which, when interrupting high current, the piston-driven compression chamber is emptied fully without using calibrated valves in the compression piston, but rather by discharging the gas into the interrupting space via a separate discharge channel, this injection of non-ionized or little-ionized gas contributing to regenerating the hot gases present in the interrupting space so as to improve the dielectric strength of the circuit-breaker during subsequent opening thereof.
To this end, the invention provides a circuit-breaker including two contacts which are disposed in an interrupting space filled with a dielectric gas under pressure and between which an electric arc strikes during circuit-breaker opening, the circuit-breaker further including a thermal blast chamber that communicates directly with the interrupting space, and a piston-driven compression chamber that communicates with the thermal blast chamber, in which circuit-breaker the piston-driven compression chamber communicates with the interrupting space via a discharge channel that is separate from the thermal blast chamber and that is closed by a discharge valve, wherein said discharge valve is disposed between the thermal blast chamber and the piston-driven compression chamber in a manner such that said discharge valve opens to enable the gas under increased pressure in the piston-driven compression chamber to be discharged towards the interrupting space via said channel when the increase in the pressure of the gases in the thermal blast chamber is larger than the increase in the pressure of the gases in the piston-driven compression chamber. Thus, with this configuration, the discharge valve is moved by the resultant force corresponding to the difference between the increase in the pressure of the gases in the thermal blast chamber and the increase in the pressure of the gases in the piston-driven compression chamber. When interrupting low current, the increase in pressure in the piston-driven compression chamber is larger than in the thermal blast chamber and the resultant force that acts on the discharge valve tends to hold it in its closed position so as to prevent the piston-driven compression chamber from emptying through the discharge channel. The gases in the piston-driven compression chamber are thus blasted into the interrupting space through the check valve, and through the thermal blast chamber. Conversely, when interrupting high current, the resultant force that acts on the discharge valve tends to move it so as to open the discharge channel, thereby enabling the piston-driven compression chamber to be emptied into the interrupting space.
In a particularly simple embodiment of the circuit-breaker of the invention, the discharge valve is a moving ring that passes through the bottom of the thermal blast chamber and through the top of the piston-driven compression chamber, and the discharge channel has an opening via which it opens out in the top of the piston-driven compression chamber. The ring is pressed against the opening in the discharge channel under the action of a return spring that works between the ring and the bottom of the thermal blast chamber. With this configuration, when the pressures in the thermal blast chamber and in the piston-driven compression chamber are equal, the ring closes off the discharge channel and prevents the piston-driven compression chamber from emptying towards the interrupting space.
In another particular embodiment of the circuit-breaker of the invention, the interrupting space is defined by a nozzle that has a diverging portion, and the discharge channel opens into the diverging portion downstream from the neck of the nozzle. This construction removes the risk of the discharge channel being blocked by the electric arc.